Blood flow-induced shear stress and, more recently, shear stress transients have been implicated as potent modulators of vascular endothelium. The overall goal of the proposed research is to establish the roles of both of these modulating stimuli at the tissue-organ physiology and cellular-molecular biology levels. The proposed work will test the hypothesis that the cell membrane may react differently to quickly and slowly changing shear stresses. To investigate this possibility at the physiological level, known membrane-modulating agents (cholesterol and alcohol) will be incorporated into endothelial cells in intact isolated arterioles to study their effects on the transduction of shear stress and shear transients into vessel dilation. These studies will have important implications for the relationship between membrane fluidity and the ability of the microcirculation to regulate organ blood flow. Second, the effects of shear and shear transients on cell membrane protein dynamics will be investigated by combining two established techniques: cell culture subjected to shear flow and fluorescence recovery after photobleaching. Such novel experiments will enable the quantification of protein and lipid diffusion during steady and unsteady shear and their roles in endothelial cell signal transduction. These studies will aid in understanding both the mechanisms of organ blood flow regulation during acute hemodynamic alterations and why atherosclerotic lesions are localized preferentially at areas of unsteady shear.